The present invention relates to weighing scales, and is more particularly directed to a device for detecting and indicating changes in a small weight that is embedded within a much larger, i.e., heavier, residual weight.
It is difficult for the consumer to measure a small variable weight that is contained within a much larger weight, most of which is a relatively constant residual weight. It is also difficult to monitor and obtain an advance warning of the impending exhaustion of a given variable weight, which can be considered a critical weight.
A weight load can be considered to consist of two or more components, that is, an initial part, a critical part, and an end part. The critical part is typically significantly smaller than either of the other two components, but this is typically the component whose weight is of the most interest. Consequently, any weighing device that detects variations, i.e., gradual depletion, of the critical component should have a more sensitive scale for the critical part than for the other two parts. In many cases, the consumer needs to monitor only the critical part, and the weighing device or scale only needs to read and monitor the critical component, and not the initial or end parts.
A particular example of this is a cylinder of a consumable gas, such as propane or natural gas. The cylinder has an empty or residual weight which does not vary for that cylinder. Also, when completely filled with propane or natural gas, the cylinder has a full or initial weight, which also is a fixed value for that cylinder. The customer is interested in monitoring the weight of the cylinder so that he or she will be aware when the contents have been nearly consumed, and the cylinder is approaching an empty condition. Where the cylinder contains, for example, ten kilograms of propane, the consumer needs to know when it has emptied down to about the final one or two kilograms, which constitute the "critical weight." Consequently, the weighing scale needs to monitor only for that range of zero to two kilograms, which lies somewhere between the cylinder's residual weight and the cylinder's full or initial weight. Thus, there is a need for a weighing device that monitors the critical part of the load.
There are many other applications as well, where the critical part of the load is embedded within the overall weight of the load, between the residual weight and the initial weight. There may also be a need to monitor the fill, rather than the depletion of a container's contents, in which case the critical weight would be increasing instead of decreasing. The critical weight range can be close to the initial weight instead of close to the residual weight.